In "wanted to welcome" I would have said "to" was part of the infinitive rather than a preposition, since prepositions are followed by noun phrases, pronouns, or -ing forms.

One of the problems in analysing English is that the same form of a word can function as different parts of speech: welcome is a prime example, acting as a noun (a welcome) or a verb (they welcome). To check whether it's acting as noun or verb substitute a word which has different forms, such as strengthen (verb) and strength (noun). We'd say wanted to strengthen rather than *wanted to strength .

Bingley

Bingley